Polyisocyanate polyaddition products produced by the reaction of isocyanates with compounds reactive with respect to isocyanates, e.g. polyols, i.e. compounds having at least two hydroxyl groups, as well as composite elements of these products with other plastics, are generally known. Stressing of these composite elements by high temperatures and atmospheric humidities often leads to an undesirable detaching of the plastics from the polyisocyanate polyaddition products. Particularly where these composite elements are used in car construction, for which such stressing cannot be ruled out, detaching of the polyisocyanate polyaddition products from the other plastics, and thus destruction of the composite element, is unacceptable.
In the production of the composite elements, and especially of the polyisocyanate polyaddition products, the problem can arise that the starting components, especially the polyol component containing the starting substances that are reactive with respect to isocyanates, do not give stable mixtures. At low temperatures, e.g. below 20° C., individual polyols can tend to flocculate in the polyol component or to sediment in the polyol component. It is important to avoid this problem for the reproducible manufacture of high-quality products.
DE-A 10 022 280 describes a process for the production of composite elements with improved adhesion and humid ageing properties of such composite materials of thermoplastics and polyurethanes. The composite is used e.g. for the production of dashboards, which are conventionally constructed e.g. from a thermoplastic support, a PUR foam and another top layer consisting of e.g. PVC, TPO, ABS, thermoplastic polyurethanes, sprayed polyurethane skins etc.
By using isocyanate prepolymers containing ester groups for the production of polyurethane foams according to DE-A 10 022 280, improved properties are obtained, in particular good adhesion between the thermoplastic and polyurethane foams of this type. When such a composite is stored in humid conditions for up to 80 hours at 80° C. and 80% relative humidity, the composite of thermoplastic and polyurethane foam is intact. After that, however, the composite separates.